Functional-structural plant modelling using a combination of architectural analysis, L-systems and a canonical model of function

This paper presents a new method for producing a functional-structural plant model that simulates response to different growth conditions, yet does not require detailed knowledge of underlying physiology. The example used to present this method is the modelling of the mountain birch tree. This new functional-structural modelling approach is based on linking an L-system representation of the dynamic structure of the plant with a canonical mathematical model of plant function. Growth indicated by the canonical model is allocated to the structural model according to probabilistic growth rules, such as rules for the placement and length of new shoots, which were derived from an analysis of architectural data. The main advantage of the approach is that it is relatively simple compared to the prevalent process-based functional-structural plant models and does not require a detailed understanding of underlying physiological processes, yet it is able to capture important aspects of plant function and adaptability, unlike simple empirical models. This approach, combining canonical modelling, architectural analysis and L-systems, thus fills the important role of providing an intermediate level of abstraction between the two extremes of deeply mechanistic process-based modelling and purely empirical modelling. We also investigated the relative importance of various aspects of this integrated modelling approach by analysing the sensitivity of the standard birch model to a number of variations in its parameters, functions and algorithms. The results show that using light as the sole factor determining the structural location of new growth gives satisfactory results. Including the influence of additional regulating factors made little difference to global characteristics of the emergent architecture. Changing the form of the probability functions and using alternative methods for choosing the sites of new growth also had little effect. (c) 2004 Elsevier B.V. All rights reserved.

Numerical simulation of magnetite segregation in a dense medium cyclone

Numerical simulations of turbulent driven flow in a dense medium cyclone with magnetite medium have been conducted using Fluent. The predicted air core shape and diameter were found to be close to the experimental results measured by gamma ray tomography. It is possible that the Large eddy simulation (LES) turbulence model with Mixture multi-phase model can be used to predict the air/slurry interface accurately although the LES may need a finer grid. Multi-phase simulations (air/water/medium) are showing appropriate medium segregation effects but are over-predicting the level of segregation compared to that measured by gamma-ray tomography in particular with over prediction of medium concentrations near the wall. Further, investigated the accurate prediction of axial segregation of magnetite using the LES turbulence model together with the multi-phase mixture model and viscosity corrections according to the feed particle loading factor. Addition of lift forces and viscosity correction improved the predictions especially near the wall. Predicted density profiles are very close to gamma ray tomography data showing a clear density drop near the wall. The effect of size distribution of the magnetite has been fully studied. It is interesting to note that the ultra-fine magnetite sizes (i.e. 2 and 7 mu m) are distributed uniformly throughout the cyclone. As the size of magnetite increases, more segregation of magnetite occurs close to the wall. The cut-density (d(50)) of the magnetite segregation is 32 gm, which is expected with superfine magnetite feed size distribution. At higher feed densities the agreement between the [Dungilson, 1999; Wood, J.C., 1990. A performance model for coal-washing dense medium cyclones, Ph.D. Thesis, JKMRC, University of Queensland] correlations and the CFD are reasonably good, but the overflow density is lower than the model predictions. It is believed that the excessive underflow volumetric flow rates are responsible for under prediction of the overflow density. (c) 2006 Elsevier Ltd. All rights reserved.

Study of flow behaviour in a three-product cyclone using computational fluid dynamics

Simplicity in design and minimal floor space requirements render the hydrocyclone the preferred classifier in mineral processing plants. Empirical models have been developed for design and process optimisation but due to the complexity of the flow behaviour in the hydrocyclone these do not provide information on the internal separation mechanisms. To study the interaction of design variables, the flow behaviour needs to be considered, especially when modelling the new three-product cyclone. Computational fluid dynamics (CFD) was used to model the three-product cyclone, in particular the influence of the dual vortex finder arrangement on flow behaviour. From experimental work performed on the UG2 platinum ore, significant differences in the classification performance of the three-product cyclone were noticed with variations in the inner vortex finder length. Because of this simulations were performed for a range of inner vortex finder lengths. Simulations were also conducted on a conventional hydrocyclone of the same size to enable a direct comparison of the flow behaviour between the two cyclone designs. Significantly, high velocities were observed for the three-product cyclone with an inner vortex finder extended deep into the conical section of the cyclone. CFD studies revealed that in the three-product cyclone, a cylindrical shaped air-core is observed similar to conventional hydrocyclones. A constant diameter air-core was observed throughout the inner vortex finder length, while no air-core was present in the annulus. (c) 2006 Elsevier Ltd. All rights reserved.

Hydrodynamics and mass transfer coefficient in three-phase air-lift reactors containing activated sludge

This study was to investigate the impacts of operating conditions and liquid properties on the hydrodynamics and volumetric mass transfer coefficient in activated sludge air-lift reactors. Experiments were conducted in internal and external air-lift reactors. The activated sludge liquid displayed a non-Newtonian rheological behavior. With an increase in the superficial gas velocity, the liquid circulation velocity, gas holdup and mass transfer coefficient increased, and the gas residence time decreased. The liquid circulation velocity, gas holdup and the mass transfer coefficient decreased as the sludge loading increased. The flow regime in the activated sludge air-lift reactors had significant effect on the liquid circulation velocity and the gas holdup, but appeared to have little impact on the mass transfer coefficient. The experimental results in this study were best described by the empirical models, in which the reactor geometry, superficial gas velocity and/or power consumption unit, and solid and fluid properties were employed. (c) 2006 Elsevier B.V. All rights reserved.

Fluidized bed gasification of biomass

A fluidized bed process development unit of 0.8 m internal diameter was designed on basis of results obtained from a bench scale laboratory unit. For the scaling up empirical models from the literature were used. The process development unit and peripheral equipment were constructed, assembled and commissioned, and instruments were provided for data acquisition. The fluidization characteristics of the reactor were determined and were compared to the design data. An experimental programme was then carried out and mass and energy balances were made for all the runs. The results showed that the most important independent experimental parameter was the air factor, with an optimum at 0.3. The optimum higher heating value of the gas produced was 6.5 MJ/Nm3, while the thermal efficiency was 70%. Reasonably good agreement was found between the experimental results, theoretical results from a thermodynamic model and data from the literature. It was found that the attainment of steady state was very sensitive to a continuous and constant feedstock flowrate, since the slightest variation in feed flow resulted in fluctuations of the gas quality. On the basis of the results a set of empirical relationships was developed, which constitutes an empirical model for the prediction of the performance of fluidized bed gasifiers. This empirical model was supplemented by a design procedure by which fluidized bed gasifiers can be designed and constructed. The design procedure was then extended to cover feedstock feeding and gas cleaning in a conceptual design of a fluidized bed gasification facility. The conceptual design was finally used to perform an economic evaluation of a proposed gasification facility. The economics of this plant (retrofit application) were favourable.

Self-selection into export markets by business services firms:evidence from France, Germany and the United Kingdom

This study investigates business services firms that (start to) export, comparing exporters to firms that serve the national market only. We estimate identically specified empirical models using comparable enterprise data from France, Germany, and the UK. Our findings show that exporters are on average more productive and pay higher wages in all three countries. However, results for profitability differ across borders, where profitability of exporters is significantly smaller in Germany, significantly larger in France, and does not differ significantly in the UK. The results for wages and productivity hold in the years before firms start exporting, which indicates self-selection into exporting of more productive services firms that pay higher wages. The surprising finding of self-selection of less profitable German services firms into exporting does not show up among firms from France and the UK. In all three countries we do not find evidence for positive effects of exporting on firm performance. © 2012 Elsevier B.V.

Construcción de índices de biomasa para los recursos anchoveta (Engraulis ringens) y jurel (Trachurus murphyi) del Ecosistema de afloramiento peruano usando modelos empíricos basados en información acústica

Los principales recursos pesqueros pelágicos de interés económico en el Perú son anchoveta (Engraulis ringens), jurel (Trachurus murphyi) y caballa (Scomber japonicus) [3]. Para su evaluación, se lleva a cabo cruceros de evaluación acústica en los que se integra información de ecoabundancia y proporción de tallas por especie para obtener valores de biomasa y abundancia. Sin embargo, para especies no objetivo (como jurel), dichos valores resultan poco confiables por la lejanía entre los puntos de muestreo biométrico y acústico. Para resolver este inconveniente, el presente trabajo propuso utilizar modelos empíricos (de tipo GAM y GLM) integrando variables ambientales y de seguimiento de desembarques con la finalidad de generar índices relativos y absolutos para anchoveta y jurel en el período de 1996-2013 dentro del área de las 200 mn frente a la costa peruana. Los resultados obtenidos realzaron la importancia de los lances de comprobación para la obtención de estimaciones robustas de biomasa. Así mismo, se observó que, para anchoveta, los modelos empíricos sí produjeron un buen índice relativo y absoluto, mejorando la utilización de la ecoabundancia por sí sola. Para jurel, sin embargo, el modelo final calibrado resultó en la obtención de un mejor índice relativo. Se recomienda además, la obtención de información de tallas y pesos medios de desembarques para jurel con la finalidad de mejorar las estimaciones de biomasa y abundancia.

Previous land use and climate influence differences in soil organic carbon following reforestation of agricultural land with mixed-species plantings

Reforestation of agricultural land with mixed-species environmental plantings (native trees and shrubs) can contribute to mitigation of climate change through sequestration of carbon. Although soil carbon sequestration following reforestation has been investigated at site- and regional-scales, there are few studies across regions where the impact of a broad range of site conditions and management practices can be assessed. We collated new and existing data on soil organic carbon (SOC, 0–30 cm depth, N = 117 sites) and litter (N = 106 sites) under mixed-species plantings and an agricultural pair or baseline across southern and eastern Australia. Sites covered a range of previous land uses, initial SOC stocks, climatic conditions and management types. Differences in total SOC stocks following reforestation were significant at 52% of sites, with a mean rate of increase of 0.57 ± 0.06 Mg C ha−1 y−1. Increases were largely in the particulate fraction, which increased significantly at 46% of sites compared with increases at 27% of sites for the humus fraction. Although relative increase was highest in the particulate fraction, the humus fraction was the largest proportion of total SOC and so absolute differences in both fractions were similar. Accumulation rates of carbon in litter were 0.39 ± 0.02 Mg C ha−1 y−1, increasing the total (soil + litter) annual rate of carbon sequestration by 68%. Previously-cropped sites accumulated more SOC than previously-grazed sites. The explained variance differed widely among empirical models of differences in SOC stocks following reforestation according to SOC fraction and depth for previously-grazed (R2 = 0.18–0.51) and previously-cropped (R2 = 0.14–0.60) sites. For previously-grazed sites, differences in SOC following reforestation were negatively related to total SOC in the pasture. By comparison, for previously-cropped sites, differences in SOC were positively related to mean annual rainfall. This improved broad-scale understanding of the magnitude and predictors of changes in stocks of soil and litter C following reforestation is valuable for the development of policy on carbon markets and the establishment of future mixed-species environmental plantings.

A new age of fuel performance code criteria studied through advanced atomistic simulation techniques

A fundamental step in understanding the effects of irradiation on metallic uranium and uranium dioxide ceramic fuels, or any material, must start with the nature of radiation damage on the atomic level. The atomic damage displacement results in a multitude of defects that influence the fuel performance. Nuclear reactions are coupled, in that changing one variable will alter others through feedback. In the field of fuel performance modeling, these difficulties are addressed through the use of empirical models rather than models based on first principles. Empirical models can be used as a predictive code through the careful manipulation of input variables for the limited circumstances that are closely tied to the data used to create the model. While empirical models are efficient and give acceptable results, these results are only applicable within the range of the existing data. This narrow window prevents modeling changes in operating conditions that would invalidate the model as the new operating conditions would not be within the calibration data set. This work is part of a larger effort to correct for this modeling deficiency. Uranium dioxide and metallic uranium fuels are analyzed through a kinetic Monte Carlo code (kMC) as part of an overall effort to generate a stochastic and predictive fuel code. The kMC investigations include sensitivity analysis of point defect concentrations, thermal gradients implemented through a temperature variation mesh-grid, and migration energy values. In this work, fission damage is primarily represented through defects on the oxygen anion sublattice. Results were also compared between the various models. Past studies of kMC point defect migration have not adequately addressed non-standard migration events such as clustering and dissociation of vacancies. As such, the General Utility Lattice Program (GULP) code was utilized to generate new migration energies so that additional non-migration events could be included into kMC code in the future for more comprehensive studies. Defect energies were calculated to generate barrier heights for single vacancy migration, clustering and dissociation of two vacancies, and vacancy migration while under the influence of both an additional oxygen and uranium vacancy.

Produção de lipídios microbianos a partir de glicerol bruto gerado na síntese de biodiesel

Diante da grande quantidade de glicerol bruto gerado na síntese do biodiesel e seu baixo valor comercial, torna-se fundamental encontrar formas alternativas para converter este substrato em produtos com valor agregado. Neste contexto, este trabalho teve como objetivo avaliar diferentes leveduras oleaginosas capazes de metabolizar o glicerol bruto, gerado como coproduto na síntese de biodiesel, visando produzir biomassa como fonte de lipídios. Todos os cultivos foram realizados em frascos agitados, em condições estabelecidas de acordo com cada etapa do trabalho, sendo obtidos dados relativos ao crescimento celular e à produção de lipídios, tratados estatisticamente conforme o propósito. Lipomyces lipofer NRRL Y-1155 apresentou diferenças significativas em relação às outras leveduras oriundas de banco de cultura, atingindo 57,64% de lipídios na biomassa. Estas leveduras apresentarem perfis de ácidos graxos diferenciados, semelhantes aos dos principais óleos vegetais utilizadas na síntese de biodiesel, com predominância de ácidos graxos poli-insaturados, especialmente ácido linoleico (68,3% na levedura Rhodotorula glutinis NRRL YB-252). O ácido gama-linolênico, um ácido graxo essencial ω6, foi detectado em todas as leveduras analisadas, sendo que na biomassa de Candida cylindracea NRRL Y-17506 chegou a 23,1%. Através de um planejamento experimental Plackett-Burman, verificou-se que as variáveis concentração de extrato de levedura e de MgSO4.7H20 demonstraram maior influência na produção de lipídios por uma linhagem silvestre de Rhodotorula mucilaginosa. Para esta levedura, a partir da análise de efeitos foi possível estabelecer a seguinte condição para a produção de lipídios: 30,0 g.L-1 glicerol; 5,0 g.L-1 KH2PO4; 1,0 g.L-1 Na2HPO4; 3,0 g.L-1 MgSO4.7H2O; 1,2 g.L-1 extrato de levedura; pH inicial 4,5; temperatura 25°C. Nestas condições conseguiu-se um teor de lipídios de 59,96% e lipídios totais produzidos de 5,51 g.L-1 . Também foi possível observar aumento no teor de lipídios da biomassa ao longo do tempo de cultivo, bem como o aumento do teor relativo do ácido linoleico, que atingiu 52%. Dentre as leveduras isoladas a partir de amostras ambientais do Extremo Sul do Brasil, a levedura identificada como Cryptococcus humicola se destacou das demais, apresentando proporção de 23,5% de ácidos graxos saturados, 14,8% de ácidos graxos monoinsaturados e 54,9% de ácidos graxos poli-insaturados, destacando-se o ácido linoleico. O planejamento Plackett-Burman foi também utilizado para esta levedura, sendo que as variáveis concentração de extrato de levedura e glicerol bruto demonstraram maior influência na produção de lipídios. Posteriormente, um delineamento composto central rotacional (DCCR) foi proposto visando à otimização da produção de lipídios. Os modelos empíricos preditivos obtidos para biomassa máxima e lipídios totais permitiram estabelecer para a produção de lipídios por Cryptococcus humicola a seguinte condição otimizada: 100,0 g.L-1 glicerol; 5,0 g.L-1 KH2PO4; 1,0 g.L-1 Na2HPO4; 4,8 g.L-1 extrato de levedura; pH inicial 4,5; temperatura 25°C. Esta condição representou um incremento de cerca de 2 vezes nos lipídios totais em relação à melhor condição estabelecida pelo planejamento Plackett-Burmann e um acréscimo de cerca de 4,8 vezes em relação às condições testadas inicialmente, atingindo 37,61% de lipídios e 8,85 g.L-1 de lipídios totais. Deste modo, os propósitos de valorização de um coproduto oriundo da síntese de biodiesel, bem como a produção de um óleo com potencial para a produção de biodiesel, foram cumpridos.

Evaluation of thermo-physical properties and drying kinetics of carrots in a convective hot air drying system

This paper presents an experimental study on the evolution of carrot properties along convective drying by hot air at different temperatures (50ºC, 60ºC and 70ºC). The thermo-physical properties calculated were: specific heat, thermal conductivity, diffusivity, enthalpy, heat and mass transfer coefficients. Furthermore, the data of drying kinetics were treated and adjusted according to the three empirical models: Page, Henderson & Pabis and Logarithmic. The sorption isotherms were also determined and fitted using the GAB model. The results showed that, generally, the thermo-physical properties presented a decline during the drying process, and the decrease was faster for the temperature of 70ºC. It was possible to verify that the Page model presented the best prediction ability for the representation of kinetics of the drying process. The GAB model used to fit the sorption isotherms showed a good prediction capacity and, at a given water activity, despite some variations, the amount of water sorbed increased with the decrease of drying temperature.

Efeitos do tratamento superficial da sílica ativa com soluções de ácidos nítrico e fosfórico em propriedades do concreto

The addition of active silica potentially improves the quality of concrete due to its high reactivity and pore refinement effect. The reactivity of silica is likely related to its charge density. Variations in surface charge alter the reactivity of the material consequently affecting the properties of concrete. The present study aimed at investigating variations in the charge density of silica as a function of acid treatments using nitric or phosphoric acid and different pH values (2.0, 4.0 and 6.0). Effects on concrete properties including slump, mechanical strength, permeability and chloride corrosion were evaluated. To that end, a statistical analysis was carried out and empirical models that correlate studied parameters (pH, acid and cement) with concrete properties were established. The quality of the models was tested by variance analysis. The results revealed that the addition of silica was efficiency in improving the properties of concrete, especially the electrochemical parameters. The addition of silica treated using nitric acid at pH = 4.0 displayed the best cement performance including highest strength, reduced permeability and lowest corrosion current

Balancing the environmental benefits of reforestation in agricultural regions

Reforestation is an important tool for reducing or reversing biodiversity loss and mitigating climate change. However, there are many potential compromises between the structural (biodiversity) and functional (carbon sequestration and water yield) effects of reforestation, which can be affected by decisions on spatial design and establishment of plantings. We review the environmental responses to reforestation and show that manipulating the configuration of plantings (location, size, species mix and tree density) increases a range of environmental benefits. More extensive tree plantings (>10. ha) provide more habitat, and greater improvements to carbon and water cycling. Planting a mixture of native trees and shrubs is best for biodiversity, while traditional plantation species, generally non-native species, sequester C faster. Tree density can be manipulated at planting or during early development to accelerate structural maturity and to manage water yields. A diversity of habitats will be created by planting in a variety of landscape positions and by emulating the patchy distribution of forest types, which characterized many regions prior to extensive landscape transformation. Areas with shallow aquifers can be planted to reduce water pollution or avoided to maintain water yields. Reforestation should be used to build forest networks that are surrounded by low-intensity land use and that provide links within regions and between biomes. While there are adequate models for C sequestration and changes in water yields after reforestation, the quantitative understanding of changes in habitat resources and species composition is more limited. Development of spatial and temporal modelling platforms based on empirical models of structural and functional outcomes of reforestation is essential for deciding how to reconfigure agricultural regions. To build such platforms, we must quantify: (a) the influence of previous land uses, establishment methods, species mixes and interactions with adjacent land uses on environmental (particularly biodiversity) outcomes of reforestation and (b) the ways in which responses measured at the level of individual plantings scale up to watersheds and regions. Models based on this information will help widespread reforestation for carbon sequestration to improve native biodiversity, nutrient cycling and water balance at regional scales.

Previous land use and climate influence differences in soil organic carbon following reforestation of agricultural land with mixed-species plantings

Reforestation of agricultural land with mixed-species environmental plantings (native trees and shrubs) can contribute to mitigation of climate change through sequestration of carbon. Although soil carbon sequestration following reforestation has been investigated at site- and regional-scales, there are few studies across regions where the impact of a broad range of site conditions and management practices can be assessed. We collated new and existing data on soil organic carbon (SOC, 0-30 cm depth, N = 117 sites) and litter (N = 106 sites) under mixed-species plantings and an agricultural pair or baseline across southern and eastern Australia. Sites covered a range of previous land uses, initial SOC stocks, climatic conditions and management types. Differences in total SOC stocks following reforestation were significant at 52% of sites, with a mean rate of increase of 0.57 ± 0.06 Mg C ha-1 y-1. Increases were largely in the particulate fraction, which increased significantly at 46% of sites compared with increases at 27% of sites for the humus fraction. Although relative increase was highest in the particulate fraction, the humus fraction was the largest proportion of total SOC and so absolute differences in both fractions were similar. Accumulation rates of carbon in litter were 0.39 ± 0.02 Mg C ha-1 y-1, increasing the total (soil + litter) annual rate of carbon sequestration by 68%. Previously-cropped sites accumulated more SOC than previously-grazed sites. The explained variance differed widely among empirical models of differences in SOC stocks following reforestation according to SOC fraction and depth for previously-grazed (R2 = 0.18-0.51) and previously-cropped (R2 = 0.14-0.60) sites. For previously-grazed sites, differences in SOC following reforestation were negatively related to total SOC in the pasture. By comparison, for previously-cropped sites, differences in SOC were positively related to mean annual rainfall. This improved broad-scale understanding of the magnitude and predictors of changes in stocks of soil and litter C following reforestation is valuable for the development of policy on carbon markets and the establishment of future mixed-species environmental plantings.

Climate, Land Use and Hydrologic Sensitivities of Stormwater Quantity and Quality in Complex Coastal Urban Watersheds

The study analyzed hydro-climatic and land use sensitivities of stormwater runoff and quality in the complex coastal urban watershed of Miami River Basin, Florida by developing a Storm Water Management Model (EPA SWMM 5). Regression-based empirical models were also developed to explain stream water quality in relation to internal (land uses and hydrology) and external (upstream contribution, seawater) sources and drivers in six highly urbanized canal basins of Southeast Florida. Stormwater runoff and quality were most sensitive to rainfall, imperviousness, and conversion of open lands/parks to residential, commercial and industrial areas. In-stream dissolved oxygen and total phosphorus in the watersheds were dictated by internal stressors while external stressors were dominant for total nitrogen and specific conductance. The research findings and tools will be useful for proactive monitoring and management of storm runoff and urban stream water quality under the changing climate and environment in South Florida and around the world.